Flashing checkerboard pattern

For the last couple of months, I have noticed that my Macbook Pro will occasionally flash a quick checkerboard pattern, for just a fraction of a second. It is usually some garish colour scheme. I'm not able to reliably reproduce the image, but it pops up a few times a week. I mostly notice it when using a web browser (not just Safari but also in Chrome), where it will pop up in a small section of the screen, usually coinciding with some video or image on a web page. Is this an issue I should worry about? Or normal behaviour? (One thought I had was that it is related to an invisible overlay on a web page or something like that.)

My major worry is that there's something wrong with the graphics output in my MBP. It is still under AppleCare, but it is such a hassle to get the work done (I don't live near an Apple Store) and my work depends on my computer. Plus, it's been in for Apple Care repairs a couple of times already.

This is a mid-2010, 13" Macbook Pro. I run Lion (10.7.2).

Thanks.